Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 180247

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1047 PM EDT Tue Oct 17 2017

Cool high pressure will move off the East Coast for the second half
of the week providing a light south to southwest flow of milder air.
Temperatures will warm a little to a few degrees above normal
through the weekend. A strong cold front will arrive early next week
which brings the coldest air so far this season.


As of 1030 PM EDT Tuesday:  Still expecting modest radiational
cooling given already light/calm winds and clear skies per latest
GOES16 nighttime products.  Thus, kept the fcst min temps as they
were, which is a degree or two below nearly all guidance sources.
Areas of frost look to be a good bet across much of western NC
along/north of I40, as well as across all of the NC mtns where the
sheltered valleys are expected to cool nicely, with only patchy
frost expected elsewhere across the region.  Therefore opted for
no changes to the current Frost Advisory.

As of 200 PM EDT Tuesday: Upper trough is pushing out of the area
but weak NW flow continues as surface high pressure settles over
the Mid-Atlantic. As we move through the near term, a shortwave
ridge will develop ahead of a deepening wiggle over the MS Valley,
which allows the surface high to remain in place over the VAs and
Carolinas. The deepening trough over the MS Valley will push east
toward the Appalachians late in the period but with no attendant
moisture, should see at best maybe a slight increase in high clouds
across the mountains, but that might be pushing it. The bigger
concern will be frost development tonight. Guidance in fairly good
agreement, but a degree or two difference in temps might result
in a larger difference in frost formation. Winds should go calm or
very near it with the surface high in place, and though the airmass
is dry, dewpoint depressions should be enough to allow at least
some dew, or for the concern in question, frost to form. Mixing
in the mountains might actually mean that some of the NW Piedmont
sees more frost than the mountains, but getting a little nitpicky
there. Have opted to expand the Frost Advisory east to include
more of the NW NC Piedmont, with a little wiggle down into Lincoln
county to catch the climatologically cooler areas there (as per
COOP MOS). Though note the overnight low temp forecast might end
up being a tad warm in some areas. With ideal radiational cooling
across the SC Piedmont, could see some patchy frost in southern
zones away from the mixing influence of the mountains/foothill,
but at this time not enough to warrant an advisory in those areas.

Continued cool (below normal) tomorrow but a few degrees warmer
than what we`ll end up seeing today, with a slight NE breeze
picking up especially across the Piedmont during the afternoon.


As of 100 PM EDT Tuesday: Llvl ridging lingers atop the region
Wednesday night. Under another night of clear skies and light wind,
Thu am mtn valley min temps will flirt within the frost range.
With weak but veering flow at 85h, mins in the higher elevations are
expected to be milder than the valleys. Upper heights atop the SE
Conus start to rise on Thursday. With another day of sunshine, max
temps will rise back to above climo. Upper ridging is progged to
build atop the region on Friday with perhaps some high clouds
topping the upper ridge and spilling in. The warming trend is slated
to continue, with solid middle 70s progged for the Piedmont.


As of 130 pm EDT: A strong 500 mb ridge azis over the southeastern
U.S. Friday night will slide off the southeast coast on Saturday.
Meanwhile, the nose of a New England surface high pressure center
will remain over the forecast area - with dry profiles and above
climo temps in place for the early weekend.

The medium range models feature relatively good agreement on the
southern stream portion of a central CONUS trough axis cutting off,
or at least becoming out of phase with the northern stream, over
east Texas on Sunday. Return flow moisture ahead of this system, as
well as around the offshore Atlantic high pressure center, will
permit clouds to steadily return to the region Saturday night
through Sunday, with deeper moisture and better forcing developing
Sunday night through Monday. Instability will also be uncovered in
southeast sections by Monday afternoon, and a thunder mention will
be included. Any shear ahead of the lifting southern tier system
looks limited, as does severe potential at this point.

A trailing strong cold fropa will move through the southern
Appalachians on Tuesday, with much cooler thicknesses starting to
spill into the region. Subfreezing 850 mb temps along with better NW
flow moisture appear timed just beyond the current forecast period
next Tuesday night.


At KCLT and Elsewhere: VFR conditions will prevail through
the taf cycle at all sites aside for at KAVL where morning mtn
valley MVFR/IFR fog is included.  Given good radiational cooling
conditions and lgt/calm flow tonight, am expecting patchy frost
to affect KAVL/KHKY, possibly affecting KCLT as well if cooling is
sufficient to overcome heat island effects.  Otherwise, light nly
flow will dominate on Wednesday amidst skc or a few high cirrus
to stream in aloft late in the day.

Outlook: Seasonably cool and overall VFR conditions will persist
through the work week with the only possible exceptions being mtn
valley fog/stratus restrictions in the morning.

Confidence Table...

            02-08Z        08-14Z        14-20Z        20-00Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     Low   52%     High 100%     High 100%
KHKY       High 100%     High 100%     High 100%     High 100%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     High 100%     High 100%     High 100%

The percentage reflects the number of guidance members agreeing
with the scheduled TAF issuance flight rule category. Complete hourly
experimental aviation forecast consistency tables and ensemble forecasts
are available at the following link:


NC...Frost Advisory from 2 AM to 9 AM EDT Wednesday for NCZ033-


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